Previous reports have described a model neurosecretory system for the in vitro secretion of norepinephrine (NE) in rat heart slices. Calcium-dependent secretion is mediated by the transport mechanism in the plasma membrane. This secretion shows various parallels with neurosecretion during synaptic transmission. It has now been shown that the Na ion-free medium mobilizes amine for immediate transport at the membrane. Amines are thus diverted from monoamine oxidase (MAO). In the presence of cocaine, which blocks release, amines are protected from MAO suggesting that they are not fully mobilized, unlike amines released by reserpine. The Na ion-free medium inhibits the massive deamination that takes place in the presence of reserpine. The results of other experiments suggest that the plasma membrane of nerve endings retain its structural integrity for hours during cold immersion at 0 degrees. Cold immersion permits the demonstration of Na ion-dependent outflow. Large molecules, like ATP can penetrate the membrane during cold immersion and block Na ion-dependent efflux. Extracellular ATP inhibits the uptake of NE.